A widely used storage medium for storing data is tape, such as magnetic or optical tape. Storage tapes can be mounted in various types of tape cassettes or cartridges. One type of tape cassette or cartridge is a two-reel or two-spindle cassette or cartridge in which the tape is housed entirely within the cassette or cartridge. One end of the tape is attached to a first reel, while another end of the tape is attached to a second reel. The cassette or cartridge is loaded into a tape drive, which includes a tape head that engages the tape to read data from or record data to the tape as the tape is wound from one reel to the other.
Alternatively, a single-reel or single-spindle tape cartridge can be used in which the cartridge has one reel or spindle. A single-reel cartridge is generally more space efficient than two-reel tape cassettes or cartridges. In a single-reel design, the source reel is located in the tape cartridge but a take-up reel is located outside of the cartridge in the tape drive.
Once a single-reel cartridge is loaded into a tape drive, the tape drive typically uses a picker or leader block to remove an end of the tape from the cartridge. The tape is then mounted onto the take-up reel inside the tape drive, and the tape is then wound from the source reel to the take-up reel. The tape end to be drawn into the tape drive is secured to an element referred to as leader pin. There are different designs of leader pins that can be employed. One such leader pin design is a leader pin assembly that conforms to a version of the Ultrium Standard, described in “Data Interchange on 12, 7 mm 384-Track Magnetic Tape Cartridges—Ultrium-1 Format,” Standard ECMA-319 (June 2001).
The tape in a single-reel cartridge includes a leader tape and data tape (for storing data), with the leader tape attached to the leader pin assembly. The leader tape is linked or coupled to the data tape by a piece of splicing tape. Generally, the leader tape is thicker than the data tape to provide strength during threading operation so that the leader tape does not break. The splicing tape is also a relatively thick tape (usually thicker than even the leader tape). As a result, abrupt transitions in tape thickness occurs at the edges of the splicing tape and at the transition from the leader tape to the data tape. As the tape is wound onto the take-up reel in the tape drive, the abrupt thickness transitions cause an imprint of bumps in the roundness of the tape pack (which includes the multiple wraps of tape that are wound onto the take-up reel). The bumps usually extend through many layers of tape, often through the entire tape pack on the take-up reel. As the tape is spooled off of the take-up reel at the end of a rewind cycle, the imprinted bumps may cause physical excitation in the tape. The physical excitation in the tape causes undesirable movement of the tape. This movement is detected by tape drive circuitry and indicated by position error signals (PES) that are used by the tape head of the tape drive to compensate for the undesirable movement of the tape.